erebion

XMPP server, do some decentralised communication under your control. It will federate to other servers, allowing you to speak to other people and join public chats. An old Raspberry Pi should easily be able to server 100 or 200 users. Try Prosody for that or Snikket if you prefer containers and everything working out of the box.

You could also use it as a NAS, if you don’t need a fast NAS. It will probably be enough to stream HD media using VLC on a cheap Android TV device/dongle.

But why? Then the users thinks “huh, weird” and goes on.

I’ve seen that countless times with people that are less technical.